Application pillar dam and movable caisson dam technology in building barrier construction to prevent sea water rising and improving flood relief at estuary rivers.
1 Application pillar dam and movable caisson dam technology in building barrier construction to prevent sea water rising and improving flood relief at estuary rivers. Pro.PhD Truong Dinh Duz; PhD Tran Dinh Hoa; MSc Thai Quoc Hien; MSc Tran Van Thai Viet nam Academy for Water resource Research. Add: 171 Tay son – Dong Da – Ha Noi Abstract: Global climate change is causing terrible disasters such as droughts, floods and sea levels rising. To overcome this disaster is much work to do, but first of all, barrier constructions are done to prevent the sea water rising and also keeping fresh water for the national economy development. Due to the characteristics of most estuaries is deep, wide and soft soil therefore traditional technology would be difficult to implement or difficulty in construction. Application pillar dam and movable caisson dam technology in building barrier construction at estuary will overcome the difficulties mentioned above, offer high performance in building, Operations, Administration and Maintenance. I. Preface From the ancient times to the present, most of river barrier works have been constructed by traditional methods. The works in reinforcement concrete bulk form with characteristics as shown: bed slab from 1m to 1,5m thick, piers are placed on the slab, the between of piers is valve gates, pile system or non pile is placed under bed slab depending on foundation geology There are 3 methods for traditional works. The first is applied for works which constructed on bank: Excavating foundation hole, Construction of sluice on bank, Diversion through original river bed, Excavating canal for connecting sluice upstream & downstream and original river after sluice constructed, then earthfill dam is embanked for closure of old river. This method is widespread in Vietnam and it is applied for works constructed on bench part of river. gate Pier Bottom pile foundation upstream apron Stilling apron Fig 1: Cross section of traditional works River Upstream Downstream soil Dam Figure 2: Traditional sluice on bank 2 The second is applied for sluices constructed on river bed: Excavating of diversion canal on right/left bank, Embankment of downstream & upstream cofferdam for closure construction site. Construction of sluice in dry foundation hole. After sluice constructed, Cofferdam must be broken out for flow running through sluice and closing diversion canal. This kind of method is done on straight parts of river. The third is applied for construction of a part of sluice in cofferdam: Embankment of cofferdam for enclosing a part of river, Construction of a part of sluice in cofferdam, Diversion through a part of remain river of original river. After completing sluice construction, cofferdam must be broken out, Diversion through constructed part of sluice, Embankment of cofferdam for construction of the remainder part of sluice. This method is used for construction of works on wide part of river. The traditional method has advantage of being easy control in construction, skill in design and construction. However, diversion construction is complex if these methods are applied to works on Mekong delta or large river regions, and the weakness which are very difficult to over come has occurred at living resident zones as : Big quantity, a lot of construction land area occupied, Environment effected, some sites are difficult for construction and high cost. The methods are difficult to apply to the regions of cropping pattern transition. II. Movable caisson dam technology The idea of technology was given from 1992 - 1994. In the year of 2003, this technology was continued to study in the ministry level subject “Design study and production of movable caisson dam for economic structure transition on the Mekong delta “. In 2004 year, the permission of experiment production with this technology was given at ministry level DAĐL- 2004/06 “Completing design production, construction and operation & maintenance of movable caisson dam which applied for construction of rive barrier works at coastal/tide regions”. This technology was applied to construct two dams in Phuoc Long – Bac Lieu (2004), Thong Luu – Bac Lieu (2005) . In 2005 year, the technology was applied for technical design of 16 sluices on the rice-growing area of Ninh Quới and for setting the feasibility study of 22 sluices of salty- sweet boundary division project at Giá Rai of Bạc Liêu province. In 2006 the design and Upstream Barrier Downstream CofferDam Diversion canal Figure 3: Construction of traditional sluice on river bed Barrier CofferDam Upstream Downstream Figure 4: Diversion sluice through river 3 construction for 7 sluices of Omon-XaNo project was applied this technology by the Ministry of Agriculture and Rural Development (MARD) and two sluices named Minh Ha &Rach Lum of Tran Van district, Ca Mau province were also successful in the year of 2007. The movable caisson dam technology was not only evaluated at the Vifotec award in 2006 and the invention exclusive right degree given in 2007, but also at the award of excellent technology among 5 awards on August 2007 given by the decision of ACECC – Asian Civil Engineering Coordinating Council. II.1 Technological principle and structure of movable caisson dam a. Principle: Slump stabilization: Application of optimal structure with light slab beam for bed stress smaller than allowable stress of weak bed, and the bed treatment is not necessary accordingly. Slide, overturning stabilize: Using bed earth friction with bed of works and sluice side earthfill with side wall. Permeable stabilization: Following the horizontal border principle under the bed of works. Erosion stabilization: Enlargement of sluice span for speed after sluice smaller than allowable erosion speed of weak original earth, and so, the simple consolidation is only necessary. b. Structure of works: Form 1 (Hermetic float box): Bed and pillar in box form with side slab structure and optimal bearing frame. Material for production of movable caisson dam is normal one such as reinforcement concrete, steel, composite. Movable caisson dam bed box is divided a lot of gallery spans. Each works can be included 1 barge with valve spacing from 4 to 30m or many barges connected each other by watertight structure depending on the width of river. Form 2 (side slab box): Bed box and pillar with side slab unit structure, both of upstream and downstream of sluice are location for installation of valve or slot, sluice body and slot at two heads, these made a box with open on face and water tight around faces, so that the sluice can be floated on the water surface and movable to construction site. Figure 5: Cross section of movable caisson dam 4 The gates using for this works can be Clape, segment, self acting, rubber, vertical lift gates… c. Construction solutions: * Caisson dam manufacture: - This dam is manufactured in factory or precast hole, or on earth mound where land clearance is not necessary. - Installation of valve gate and operation equipment. - Diversion water into precsat hole to float dam to construction site. * Erection work: - Excavation of foundation hole: - Chief cost price, expenditure for the dam is less 40% than traditional works in the same condition. Investment level for traditional method is around 800 million VND per 1m sluice while only 250 million VND per 1 m sluice for caisson dam technology. Taking Phuoc Long dam in Bac Lieu province as one example on its price of 8 billions VND for traditional method and only 2.3 billions for caisson dam technology. - The method has both of science and economic significances on caisson dam’s movable ability in case of changing construction site by crop production transition demand, and it can be reused works structure, even expenditure is not necessary for breaking out work . - Backward dam can be replaced by temporary one but it will be waste and environment pollution, during only 10 years of dam management, the expense for temporary dam is the same expenditure as for construction of one movable caisson dam. b. Technical output: - Movable caisson dam technology has opened one more new direction of river barrier technology and promoted new technology development in construction of river barrier works. - Using bearing ability of original bed for works construction without weak foundation treatment costly. - Optimizing its structure, saving materials, Thông Lưu dam as one example. It was constructed with traditional method with around of 1500m³ reinforcement concrete, but with movable caisson dam technology, the Thong Luu dam was completed with the amount of 180m³ reinforcement concrete - Quick construction, reducing land area occupied by project site. - Stable project and easy in O & M work - Movable caisson dam can be manufactured and erected according to technology nature. c. Social output: Figure 6: Phước Long dam for salty protection 5 - This dam is constructed and erected on river, so that it is not necessary to move houses, make compensation…If traditional method was applied in dam construction, the above-mentioned work must be done. - The new technology should meet tide zone economic development requirement for improving living standard and contributing on social stable at coastal regions. -The new technology brings higher output in construction at underdevelopment transportation zones material transportation is very difficult at zones with complex natural topographic conditions as Ca Mau peninsula where is remote area. - Movable characteristic of caisson dam meets open planning, future economic development for contributing the national agricultural modernization. - Environmental pollution is not occurred at zones where broken out temporary dam. Natural environmental landscape is not changed by using movable caisson dam technology (construction diversion and plan are not need to be done…). - Environmental protection and flood drainage capability at caisson dam site are better than traditional and temporary dam sites by spacing open. - The types of present works and difficulties at Ca Mau peninsula can be solved by movable caisson dam technology but not by others. III. Pillar dam III.1. Definition of pillar dam Pillar dam is type of works on river, its duty is water source regulation. Pillar dam is constructed on river bed. The water drainage and river bed are about the same width, bearing by pillar laid on pile system, beam supports valve which placed on two pillars, permeable protection by grooved pile under valve supported beam erosion protection by rock cover. Water pressure by the difference between upstream and downstream which is received by valve gate and together with loading capacity on bridge, all, transmitted into pillar, then continued down to foundation pile system. Such type of works for water barriering and regulation is called pillar dam. III.2.Design principle of pillar dam 1. Works stable by pile system fixed into earth bed of river. It can be used reinforcement concrete, pipe, or filling piles depending on field conditions. Pillar dam is bearing big vertical loading capacity, because of in pillar dam there are a lot of piles for bearing cross loading Fig. construction of sluices in foundation hole Cà Mau 6 capacity. Consequently, the construction of pillar dam should be combined with construction of bridge. 2. Permeable protection according to the principle of sheet pilling vertical bounder, but not bed sheet. 3. Enlarging sluice span for increasing flood drainage capacity, flow speed is reduced and equal delivered at tail of downstream in order making it smaller permissive scouring flow speed of bed earth, so that spillway consolidation can be minimized (consolidation by rock cover is enough). Sluice is placed on right main flow, construction diversion through river, it is no need to construct dam for river closing and diversion canal. Quantity of land compensation is less. III.3. Structure of Pillar dam a. Supported pillars The pillar is main bearing component which made by pile system. This system is fixed into bed, the pile can be compacting, filling. Supporting is placed on the pile system, pillar is placed on the supporting. Spacing between pillars is from 5 m to 40m depending to field requirement. Supporting pillars are constructed in flow by blockade of steel slab pile supporting frame, coffer dam is not round embanked and construction diversion canal is excavated. Structure of supported pillar is shown in fig. 8. b. Beam supporting valve. Structure of the beam is single one, the beam is chocked on two pillars, it receives a part of water pressure from valve gate and the pressure is transmitted into supporting pillar, beam supporting valve together with two pillars at both sides make 3 faces against valve gate. Beam supporting valve can be precasted on dry place, then, put together into position or in-situ beam in blockade of steel slab pile supporting frame. c. Permeable protection component pile foundation Antiseepage upstream apron Lowerbeam Gate Figure 8: Cross section of pillar dam 7 Dam permeable is protected by groove slab fixed deeply into bed earth following stand permeable bounder. The groove is made of steel, steel covered composite or reinforcement concrete. Groove is compacted along river cross section, under supporting pillar, valve site and on bedside where much permeability. Edge of groove surface is connected with valve supporting beam tightly. Two types of permeable protection: Type of coupling into water. Two holes on pillar are remained for installation of groove supporting beam. Groove for permeable protection is compacted at the centre of two groove supporting beams and two ears of groove are chocked on these beams which make the same height for grooves for water tight between groove head and valve supporting beams. All of groove piles, valve & valve gates make a water tight plane which separates upstream and downstream of sluice. Type of construction in place Type of valve beam is constructed in place at surround frame, groove supporting beam is not necessary but the head of groove pile is connected directly into valve supporting beam concrete. d. Structure of scouring protection Width of pillar dam is nearly the same as river’s, so the water level difference between before and after dam of flood flow is very small. Flow through pillar dam is nearly the same bridge’s, flow speed is nearly the same river’s, therefore long, thin concrete reinforcement spillway as traditional structure is not necessary but method of flow consolidation by rock cover is necessary for protection of before and after sluice connection part which effected by vortex flow after dam pillar. Downstream is not effected by scouring with the condition to be V ≤ [V]. in which V is after dam flow mean speed, [V] is permission non-erosion speed of bed earth. Erosion protection textile is spread directly on bed surface at upstream and downstream sides. Beams and concrete reinforcement frames are used to keep the textile, Erosion protection concrete slabs, rock covers can be used to make diffuse walls by concrete beams which lay on piles. e. Valve gate and control devices Figure 9: T type of putting together construction Figure 10: In-situ construction type 8 The type of valves such as Clape, buoy can be used for intercepting dam with type of pillar. Rotation axis is under these valves, When valve opens , its axis is bed earthen , it is not obstacle for flood discharge and it is not effected by floating, windy, waves and plane, automatic, radial valve gates can be used. For type of rotation axis under valve, its axis is fixed into valve supporting concrete reinforcement beam to transmit bearing down and reduce moment which impacts on supporting pillar, thus pillar size is reduced. Spacing of these vales can be enlarged to be 20÷40m, but it is difficult for reparation work. III.4. Construction method - Construction under water. The hammer with its capacity of 2.5 – 3.5 ton is used to compact piles on floating platform, this hammers are used widespread in Viet Nam. For big dams, supporting pillar foundation can be treated by big dimension pipe or filling pipe. - Construction of pile platform and supporting pillar are done in steel slab around frame or face down bucket - Permeable protection groove piles are done under water by crane, compacted hammers (Shake hammer can be combined) on floating platform. - Valve supporting concrete reinforcement beam is placed in site (at location of each dam span) or on floor, then using jack, winch, and crane to move them down to their position. Steel standard framework should be used to reduce errors in construction of concrete, pile framework system, pillar framework and supporting beam framework. - Valve gate and rotation axis supporting steel framework: comprehensive installation of valve gate is done before moving them to their location by crane, winch, and kick on floating platform or floor. - Transportation bridge beams are installed by crane laying on barge or one kind of beam plunge machine. III.5.Design works following pillar dam and its economic output - Phó Sinh sluice in Bạc Liêu province consists of 3 automatic valve gate spans, width of each gate is 7.5m. Difference of water level is 3m. Transportation bridge with H13-X60. This works is only experimental one on bearing structure principle of pillar dam, the permeable protection and construction method are the same as traditional sluices. II Figure 11: Cross section of Dinh river Dam in Ninh Thuan province 9 - Cui river sluice consists of 2 gates, width of each gate is 7.5m. the difference of water level is 3m. All of principle and idea of pillar dam are experimented, its construction is carried out under water. However, its economic output is not so high by its size is small. - Hiền Lương sluice in Tư Nghĩa district, Quảng Ngãi province, its cost is 200 million VND per/1 .0 m wide. Hiền Lương sluice has span with 64m wide, the sluice consists of 16 automatic gates with 4m wide for each, water level difference is 2m, bridge 4m, H13-X60. Total cost is 11 billions VND, Cost saving is 12 billions VND. - Thao Long weir in Hue city with its biggest size in Viet Nam consists of 15 spans, Bxh = 480.5x4m, bridge spacing is 33m, bridge surface is 10m, weight H30-XB80. Clape valve with its under axis of 31.5m wide, water level difference is 1.2m. Control by hydraulic cylinder, construction cost is 115 billions DVN and this method is 100 billions less than traditional method. Figure 12: Completed Thảo Long Dam - Year of 2006, the institute was commissioned to apply the technology for 7 O Mon - Xa No works instead of designed traditional works but it is very difficult to have plane for construction in Can Tho province by the Water resources construction and investment board No.10 under the Ministry of Agriculture and Rural development (MARD). III.6. Advantages of pillar dam: - Be sure of with works is nearly the same flood discharge capacity as without works, it means that environment is little changed due to upstream without inundation. Thanks big flood discharge section, so downstream river is nearly not changed. - Works is constructed right on river, cofferdam and diversion are not necessary to construct, therefore, permanent and temporary land compensation is not necessary. - Construction of works can combine with construction of big size water resources and walk Transportation Bridge works, so social-economic aspect is meaningful, and separation in construction is protected in order protection of lavish money in infrastructure construction. - Reasonable structures are applied, build quantity is reduced accordingly, the river is larger, the cost is cheaper. 10 III.7. Conclusion In the situation of the water resources which will be able to be limited by increasing demand of water using at upstream of Red and Cuu Long rivers. On other hand, the climate on the earth is hotter and hotter, thaw on North Pole, sea water level rises high, and it is estimated that in the year 2050, sea water level will be able to be risen from 35cm – 50 cm. According to forecasting, Vietnam is one among five countries to bear big loss when sea water level rising. The salinity intrusion protection and fresh water storage works should be constructed to against heavy losses by phenomenon of slump earth and sea water level rising. On the base of the above- mentioned results, from now on, this technology will be studied completely to barrier large river estuarine and deep water head as Ham Luong, Cai Lon rivers. Reference [1] Pillar dam experimental production project report; Thao Long project design profile; Movable caisson dam experimental production project; movable caisson dam subject. . Application pillar dam and movable caisson dam technology in building barrier construction to prevent sea water rising and improving flood relief at. land clearance is not necessary. - Installation of valve gate and operation equipment. - Diversion water into precsat hole to float dam to construction